1. Field of the Invention
The present invention relates to a deposition method, and more particularly to a method for atomic layer deposition.
2. Description of the Prior Art
Atomic layer deposition (ALD) is a method using self-liming reaction to deposit monolayer layer by layer on the surface of the substrate. Therefore, atomic layer deposition is able to fabricate large area thin films which are ultrathin and conformal. Doping different atoms with different features to thin films can change electronic characteristics of the films and thus broaden range of applications thereof.
Referring to transparent electrodes of ZnO-doped Gallium (ZnO:Ga) in FIG. 1 and FIG. 2, for example, the symbol Pump shown in FIG. 1 represents the time sequence for evacuating the reaction chamber. A conventional doping method of atomic layer deposition is that passing the precursor PreA with Oxygen included and the precursor PreB with Zinc included into the reaction chamber to form the ZnO layer 101 and subsequently passing the precursor PreA with Oxygen included and the precursor PreC with Gallium included into the reaction chamber to form the Gallium Oxide layer 102. Purge gas (PG) can be chosen to be passed into the reaction chamber to remove the excess precursor PreA, PreB, PreC and/or reaction byproducts. After repeating the above-mentioned process to grow sandwich structure with specific proportion of the ZnO layer 101 and the Gallium Oxide layer 102 on the surface of the substrate 10, annealing process is used for diffusing the atoms over the whole film. However, annealing process not only increases production cost and energy consuming, but it is easy to form defects, for example, vacancy, dislocation or misfit and so on; it could be seen that annealing parameters are hard to control. Additionally, annealing process with high operating temperature cannot be applied to manufacturing electrodes on organic substrates.
In summary, developing technique of atomic layer deposition to fabricate doped thin films without annealing process is a current issue.